Geotextiles are used as filter blankets underneath revetments. Their purpose is to prevent erosion caused by the energy of waves and currents and to allow free two-way flow between the water body and the ground without the build up of hydraulic pressure. Geotextiles replace partly, or completely, expensive mineral filter layers. The construction of breakwaters, small piers, coating on pipes and in-sea facilities, and small sections within the rivers are other applications of woven and non-woven geotextiles.